SIL Safety Manual
D103401X012
ED, ES, ET, EZ, HP, HPA Valves w/ 657/667 Actuator
November 2011
7
SIL Capability
Systematic Integrity
Figure 2. exida SIL 3 Capable
Fisher ED, ES, ET, EZ, HP, and HPA valves have met manufacturer design process requirements of SIL 3. These are
intended to achieve sufficient integrity against systematic errors of design by the manufacturer. A SIF designed with
this product must not be used at a SIL level higher than stated without “prior use” justification by the end user or
diverse technology redundancy in the design.
Random Integrity
The ED, ES, ET, EZ, HP, or HPA valves are classified as Type A devices according to IEC 61508, having a hardware fault
tolerance of 0. The complete final element subsystem, with a Fisher valve as the final control element, will need to be
evaluated to determine the Safe Failure Fraction of the subsystem. If the SFF for the entire final element subsystem is
between 60% and 90%, a design can meet SIL 2 @ HFT=0.
Safety Parameters
For detailed failure rate information refer to the Failure Modes, Effects and Diagnostic Analysis Report for the ED, ES,
ET, EZ, HP, or HPA valve.
Connection of the Fisher ED, ES, ET, EZ, HP, or HPA Valve to the SIS
Logic
-
solver
The final element subsystem (consisting of a positioner, actuator, and ED, ES, ET, EZ, HP, or HPA valve) is connected to
the safety rated logic solver which is actively performing the Safety Function as well as any automatic diagnostics
designed to diagnose potentially dangerous failures within the ED, ES, ET, EZ, HP, or HPA valve , actuator and any other
final element components, (i.e. Partial Valve Stroke Test).